Concentric’s geoscience team was retained to oversee the removal of a former heating oil UST adjacent to a multi-unit, low-rise residential building in downtown Ottawa. Concentric’s geoscience specialists identified data gaps in previous environmental studies completed at the site and completed a borehole investigation in concert with the tank decommissioning. Petroleum impacts were identified and delineated beyond the UST excavation, extending underneath the building. A remedial action plan was implemented involving a combination of excavation, in-situ chemical oxidation treatment of the excavation with catalyst persulphate and injections of oxygen releasing material and liquid activated carbon. Concentric’s geoscience team coordinated the remediation contractor, undertook post-remedial monitoring and liaised with regulatory bodies.